Water-soluble films made of polyvinyl alcohol or the like are used for various applications. Examples of such films include hydraulic transfer base films which are to be used for hydraulic transfer method. The hydraulic transfer method is a process in which a printed film for hydraulic transfer, which includes a water-soluble hydraulic transfer base film having on a surface thereof a print layer to be transferred, is floated on the surface of water with its print side up and then various types of shaped articles, which are transfer receptors, are pushed downward into the printed film; thereby the print layer is transferred to the transfer receptors due to hydraulic pressure (see, for example, patent reference 1). Using the hydraulic transfer method, it is possible to impart design to the surface of a shaped article having an uneven three-dimensional surface or a curved surface or to form a print layer for the purpose of improving surface properties.
In many cases, a water-soluble film produced is wound up into a roll to form a water-soluble film roll. The water-soluble film roll is packed up and then transported to a secondary-processing manufacturer or the like. The water-soluble film roll, which has been unpacked there, is then installed to a paying out machine and is subjected to secondary processing, such as printing.
In application of secondary processing, particularly of high-speed printing, occurrence of film rupture during the paying out of a film from a roll thereof has become a problem. In a processing line of a continuous system, production loss is caused mainly by rupture of a film because it takes a long time to reintroduce a film to a processing machine. Rupture of a film may occur throughout a year, but it occurs particularly frequently in winter.
It has heretofore been believed that occurrence of film rupture is greatly influenced by moisture. Therefore, approaches of packing or wrapping of water-soluble film rolls sufficiently have been adopted. In many cases, however, it is impossible to avoid occurrence of rupture of a film during the paying out thereof no matter how the packing or wrapping thereof is sufficient.
Meanwhile, it has been believed that the reason why rupture of a film occurs particularly frequently in winter is that tear strength of a film decreases when the temperature of the film is low. Therefore, a countermeasure is taken which includes use, in winter, of a water-soluble film softened through adjustment of the composition of the base resin of the film. Nobody, however, has exterminated rupture of films.
Patent Document 1: JP 54-33115 A